How to flush your irrigation lines?

Flushing constitutes an important maintenance routine. In micro-irrigation systems, provisions must be made to flush mains, submains and lateral lines to remove settled sediments.

Mainline should be flushed at scour valve locations, whilst submains are flushed at slushing points usually located at the ends of the lines while the system is running and allow water to run into a container until it runs clear. Collect some of the dirty water in a glass or clear plastic container and examine the contaminants.  Take note of the nature of the impurities in the water. If there be a significant amount of contaminant in the flush water, find out what it is.  Does it appear to be bacterial slime? Are large aggregated particles present? Is there evidence of iron precipitation? Is there any material that could be sand from the media filter?

If unsure, have water examined and take corrective action to cure the problem. If chlorine or acid treatment is required follow the steps below for treatment.

Please note whenever a repair has been carried out on any pipe work in the system, flushing and cleaning of filtration will have to be carried out.

At the end of the season empty mainlines, field filters and valves and ensure all ball valves are opened to drain the water from within the ball and then shut again to prevent vermin and contaminants entering the system. This draining of components will help in preventing frost damage.

Chlorinating the system

Chlorination is recommended to reduce blockages due to organic matter. Chlorine is an oxidising agent that kills bacteria, algae and other organic matter and prevents new growth.  Certain bacteria cause iron to precipitate and form a red filamentous sludge that attaches to pipes and may block emitters (sprinkler nozzles as well as drippers).  Continuous injection of chlorine prior to the filter, at the rate of 0.5 ppm to 1 ppm, can also be used to precipitate the iron and prevent it moving past the filter.

The most common chlorine compounds are sodium hypochlorite (liquid) and calcium hypochlorite (solid).  Sodium hypochlorite (10% chlorine) is easier to use and relatively safe.

There are four main chlorine application methods:-

  • intermittent treatment
  • continuous treatment
  • superchlorination
  • end of season chlorination


The procedures below should be used as a guide to developing a procedure that suits your system, water conditions and management.

Intermittent treatment involves periodic sterilisation by chlorination and can also be used to prevent a build-up of organic matter in the system.  This is the most commonly used preventative treatment. 30 ppm chlorine is injected 3 – 4 times during the season.

Continuous Treatment uses a constant injection rate, usually of 5 to10 ppm, adjusted so that 1 ppm of chlorine is detectable at the end of the furthest lateral from the pump. A swimming pool tests kit can be used to detect the chlorine and its level.

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